1. Field of Invention
This invention relates generally to regulating valves to control fluid flow, and more particularly to a pressure regulating valve supplied with a pressurized liquid whose pressure varies, the valve yielding a liquid having a substantially constant pressure level.
2. Status of Prior Art
A regulating valve derives its power of operation from the fluid being controlled and functions to hold constant a fluid quantity, such as pressure or flow velocity. While the invention resides in a regulating valve yielding a fluid having a substantially constant pressure and a valve of this type has many practical applications, a valve in accordance with the invention will be described herein in connection with a backpack spraying equipment, for in this context the valve has particular value. It is to be understood, however, that the valve is by no means limited to this application.
Suppliers of agricultural chemicals, such as insecticides, herbicides and fungicides in liquid form, have developed specific guidelines for the safe and effective use of these chemicals in order to satisfy requirements mandated by law. Typically, users of backpack spraying equipment must adjust their system for different product uses. This is done by installing a nozzle, a spray tip, or wand designed to afford the desired spray coverage. These nozzles or wands have different orifice sizes which when fed liquids at a certain pressure will then allow a calculable flow rate.
Backpack spray systems in current use are capable of producing liquid pressures for use up to 70 PSI. A hand-operated pump mechanism coupled to a small pressure chamber inside the backpack reservoir is used by the operator to maintain a satisfactory working pressure during applications of the liquid. Though this arrangement allows a user to quickly reach an acceptable working pressure and to begin spraying, it demands frequent pumping, and this gives rise to varying pressures.
Since flow rate is a function of both liquid pressure and the size of the orifice through which the liquid is discharged, backpack spray systems currently in use inherently produce varying flow rates. As a consequence, the user of the system has little control over the delivery of the chemicals being sprayed, and an excessive or an inadequate application of the chemicals is then difficult to avoid.
Many backpack spraying systems in current use are provided with a wand having a shut off valve, the wand being coupled to the liquid chemical reservoir in the backpack which includes a hand-operated pump mechanism. Should the operator open the spray wand valve before the system has been pumped to a satisfactory working pressure, the liquid will not then be sprayed out of the wand, but will instead drip, dribble or leak out of the wand and be deposited anywhere but on its intended target. The reason for this leakage is that when liquid is fed to a spray nozzle, it will only atomize and emerge as a spray when the pressure of the liquid is at a relatively high level. Should the pressure fall below this level, it will simply leak out of the nozzle.
This leakage of chemicals is not only wasteful, but it may also be hazardous if the leaked liquids make contact with the operator's skin or clothing. Such leakage can also occur if during a spraying operation the liquid pressure drops below a level at which the liquid atomizes.